Networks-on-chip have been proposed to enable the integration of heterogeneous SoCs in a power-efficient and scalable way. We present Ventti, a design and simulation environment that combines a virtualized platform, a NoC synthesis tool, and a library of NoC building blocks characterized at different abstraction levels. By efficiently simulating complex application scenarios running on top of Linux, Ventti enables the evaluation of alternative NoC architectures and the derivation of a final RTL implementation that meets the communication requirements while optimizing power dissipation. Experimental results demonstrate the features of Ventti and illustrate the trade-offs in terms of simulation time and power-estimation accuracy.